|Model of root growth|
The availability of plant nutrients for roots is controlled by factors such as soil properties, root characteristics, and interactions with surrounding microorganisms. Traditional soil testing techniques measure the availability of nutrients in the general soil, but this may differ from the nutrient concentration in the immediate vicinity of the root (the rhizosphere). Nutrients with restricted mobility in the soil (such as P, K, zinc, iron, manganese, and copper), may be in adequate supply in the bulk soil, but their concentration may be low near the root if the movement in the soil is too slow to replenish the nutrients entering the root.
|Calcium deficiency results in damaged root tips|
|Rhizosphere soil on wheat roots|
• Changes in Root Structure: Plants growing in a low-P soil tend to direct more of their photosynthate energy to root development and often have more fine roots with a small diameter, resulting in a larger surface area. A large root surface area allows plants to access more of the soil and scavenge any soluble phosphate that may be present.
• Enzyme Release: In low-P conditions, plants generally increase the production of enzymes that enhance the rate of P release from soil organic matter. The phosphatase enzymes are not effective in mineralizing phytate, the dominant form of organic P in many soils. Phytase, the enzyme responsible for phytate hydrolysis, is primarily released by microorganisms, which indirectly improves the P availability for nearby roots.
|Root hairs increase surface area|
|Cross section of rice roots (notice the aerenchyma, the air channel that allows gas exchange between shoot and root)|